1. Field of the Invention
The present invention generally relates to a mounting for a load cell and, more specifically, to a load cell mounting method and apparatus to facilitate accurate measurement of an automotive brake cable tension.
2. Description of Related Art
In automobile manufacture, automotive parts are routinely tested. The parts are tested during the research and development stage of automotive design, and the parts are tested later for quality assurance purposes.
In a test of an automotive brake system, a brake cable in a brake assembly is tension loaded. The tension load on the brake cable is measured to determine the tension load applied to the brake cable at the brake handle and the tension force delivered to the brake assembly. These two tension measurements are used to determine the efficiency of the brake cable assembly and to determine whether sufficient braking force is delivered to the brake assembly by the brake cable.
It is desirable to produce an accurate proportional relationship between the strain on the brake assembly and the applied load, and thereby to measure the absolute tension transferred by the brake cable to the brake assembly. However, factors such as non-linearity, hysteresis and temperature effects on a load cell can create errors and decrease the accuracy of the measurement.
Non-linearity errors are the result of the brake cable being misaligned with the device that is provided to measure the tension on the cable. Such non-alignment creates side tension loads that are at angles to the axis of the cable. These side loads have several vector components. A first vector component is parallel to the axis and contributes to the axial tension load. However, other vector components are skewed from the axis and do not add to the axial tension load. Introduction of such side loads will result in incorrect measurements of the forces applied to the brake assembly. As such, during testing of brake cable assemblies, misalignment of testing components is a common source of measurement error.
Therefore, there exists a need in the art for a method and assembly to accurately align the brake components and, more specifically, the testing components, so as to eliminate the effects of side loading and thereby obtain more accurate measurement of tension forces on the brake cable at the brake assemblies.
The present invention is directed toward a method and assembly to accurately align the testing components with an axis of a brake cable. The present invention is further directed toward a method and assembly to eliminate the effects of side loading on a brake cable so as to accurately measure the tension force applied by the brake cable.
The present invention provides a load cell alignment apparatus for aligning a load cell during testing of a brake cable assembly. The apparatus includes a mounting structure, and an alignment structure secured between the mounting structure and the load cell. The alignment structure ensures that only axial tension is applied to the load cell during a testing procedure.
The present invention also provides a method of automatically aligning a load cell on a load cell axis during a tension test of a cable. The method includes providing an alignment structure that automatically aligns the load cell on the load cell axis during application of a tension load. The method also includes applying a tension load to the load cell and using the applied tension to automatically align the load cell and cable on the load cell axis.
The present invention further provides a method for measuring a brake cable efficiency. The method includes applying a first force to a brake handle so as to create a second, subsequent force at a brake hub. The first force and the second force are measured. The first and second force measurements are compared to determine the brake cable efficiency.